My (Accidental) Path to Forking Compound V3 for Stablecoin Dominance

Learn how I fumbled my way into forking Compound V3 to build a custom stablecoin lending protocol. Avoid my mistakes & build your own!
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8 min read
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Mark
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DeFi

Okay, full disclosure: my initial goal wasn't exactly to fork Compound V3. I was trying to quickly prototype a custom stablecoin lending protocol for a client last Tuesday. I naively thought, "How hard could it be?" Famous last words, right? I ended up diving deep into the Compound V3 codebase, and after countless hours (and a mountain of coffee), I not only forked it but also learned a ton in the process.

If you're looking to create your own lending protocol with a custom stablecoin, or just want to understand how Compound V3 works under the hood, I'm going to walk you through the exact steps I took. I'll even point out the pitfalls I fell into, so you don't have to repeat my mistakes. Believe me, there were plenty.

Why Compound V3? My Initial Reasoning (and a Few Regrets)

When I started, I considered building everything from scratch. Total madness. Then I looked at other lending protocols. Honestly, Compound V3's architecture appealed to me the most (eventually!). The isolation mode and focus on risk management were key for what my client needed. Plus, their documentation is relatively decent, which is a huge win in the DeFi space.

That said, working with Compound V3 isn't a walk in the park. It's complex, and the documentation, while good, isn't always perfect. There were times I wanted to throw my laptop out the window. But stick with me, and I'll help you avoid those moments.

Setting Up Your Development Environment: The Foundation of Sanity

Before you even think about touching the code, make sure your development environment is set up correctly. I can't stress this enough. I wasted an entire afternoon because I was using the wrong version of Node.js. Don't be like me.

Here's what you need:

  • Node.js: Version 16 or higher. I prefer using nvm (Node Version Manager) to manage different Node versions.
  • npm or Yarn: Package managers for installing dependencies. I prefer Yarn because it's generally faster.
  • Hardhat: A development environment for compiling, testing, and deploying smart contracts. We'll be using this extensively. Install it globally: npm install -g hardhat or yarn global add hardhat
  • Git: For version control. You should be using Git anyway, but seriously, use Git.

Pro Tip: Make sure your environment variables are set correctly. This can save you a lot of headache later. I even wrote myself a script to check them automatically before running any tests.

Forking the Compound V3 Repository: The Official Starting Point

Okay, time to get our hands dirty. The first step is to fork the official Compound V3 repository on GitHub. Go to the Compound V3 GitHub repository and click the "Fork" button.

Once you've forked the repository, clone it to your local machine:

git clone https://github.com/YOUR_GITHUB_USERNAME/compound-v3.git
cd compound-v3

Now, install the dependencies:

yarn install

This might take a few minutes. Go grab a coffee. Or, you know, start writing that script to check your environment variables.

Understanding the Compound V3 Architecture: A Bird's Eye View

Before you start making changes, it's crucial to understand the architecture of Compound V3. It's… involved.

Here's a simplified breakdown:

  • src/contracts/Comet.sol: The core contract for managing lending and borrowing. This is where most of the action happens.
  • src/contracts/Tokens/: Contains the token contracts used in the protocol (e.g., WETH, USDC).
  • script/: Contains deployment scripts and other utility scripts.
  • test/: Contains the tests for the protocol. This is essential. You need to write tests for any changes you make. Seriously.

(Diagram of Compound V3 Architecture - Placeholder)

I spent a good day just reading through the code and trying to understand how everything fit together. Don't skip this step! It will save you a ton of time later. I wish I had spent even more time upfront to really grok everything before diving in.

Implementing Your Custom Stablecoin: The Heart of the Project

Here's where things get interesting (and potentially frustrating). You need to create a contract for your custom stablecoin. For this example, let's call it "MyStablecoin" (MSC).

Create a new file in the src/contracts/Tokens/ directory called MyStablecoin.sol. Here's a basic example:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract MyStablecoin is ERC20 {
    constructor(uint256 initialSupply) ERC20("MyStablecoin", "MSC") {
        _mint(msg.sender, initialSupply);
    }
}

This is a very basic ERC20 token. You might want to add more features, such as:

  • Minting and burning functions: Controlled by an admin.
  • Pausing functionality: For emergency situations.
  • Governance mechanisms: For community control.

Important: Make sure your stablecoin is properly collateralized. This is beyond the scope of this tutorial, but it's crucial for the stability of your protocol. I've seen protocols crash and burn because they didn't think this through.

Modifying the Comet Contract: Integrating Your Stablecoin

Now, you need to modify the Comet contract to allow lending and borrowing of your custom stablecoin. This is the trickiest part.

First, you need to add your stablecoin to the list of supported assets. Locate the assets array in the Comet contract.

// Example: Adding MyStablecoin to the assets array (Simplified)
address public constant MY_STABLECOIN_ADDRESS = 0xYourStablecoinAddress; // Replace with your actual address
address[] public immutable assets;

You'll also need to update the constructor of the Comet contract to include your stablecoin. I spent 3 hours debugging this because I forgot to update a related mapping.

constructor(address _owner, address _baseToken, address[] memory _assets) {
  owner = _owner;
  baseToken = _baseToken;
  assets = _assets;
}

You'll also need to implement the logic for depositing, withdrawing, borrowing, and repaying your stablecoin. This involves modifying the supply() , withdraw() , borrow() , and repay() functions.

This is where understanding Compound V3's internal workings is absolutely crucial. You'll need to understand how the protocol handles risk management, liquidation, and interest rates.

I'm not going to provide the exact code for these modifications because it depends on your specific requirements. However, I will give you some general guidelines:

  • Use the existing code as a template: Look at how the other assets are handled and adapt that logic to your stablecoin.
  • Write extensive tests: Test every possible scenario. Test edge cases. Test everything.
  • Be careful with gas optimization: Gas costs can quickly add up, especially with complex lending protocols.

Deployment and Testing: The Moment of Truth

Before you deploy your modified Compound V3 protocol to a live network, you need to test it thoroughly. This is where Hardhat comes in.

Compound V3 already has a comprehensive test suite. You should add your own tests to cover the changes you made.

Here's an example test case:

// Example Hardhat test (Simplified)
const { expect } = require("chai");
const { ethers } = require("hardhat");

describe("MyStablecoin Lending", function () {
  it("Should allow users to supply and borrow MyStablecoin", async function () {
    const [owner, user] = await ethers.getSigners();

    // Deploy MyStablecoin contract
    const MyStablecoin = await ethers.getContractFactory("MyStablecoin");
    const myStablecoin = await MyStablecoin.deploy(1000000);
    await myStablecoin.deployed();

    // ... Deploy Compound V3 contracts and configure them ...

    // Supply MyStablecoin
    await myStablecoin.connect(user).approve(comet.address, 1000);
    await comet.connect(user).supply(myStablecoin.address, 1000);

    // ... Borrow MyStablecoin ...

    // ... Check balances ...
  });
});

Run your tests using Hardhat:

npx hardhat test

If any tests fail, fix them before proceeding. Deploying a broken protocol is a recipe for disaster.

Once you're confident that your tests pass, you can deploy your protocol to a testnet (e.g., Goerli or Sepolia). Use the deployment scripts in the script/ directory.

Remember to verify your contracts on Etherscan. This makes your code transparent and auditable.

Common Pitfalls and How to Avoid Them: Learning from My Mistakes

Okay, I'm going to share some of the mistakes I made along the way. Hopefully, this will save you some time and frustration.

  • Incorrect environment variables: As I mentioned earlier, make sure your environment variables are set correctly. I wasted an entire afternoon because I had the wrong API key.
  • Gas optimization: Gas costs can be a killer. Use gas optimization techniques to reduce the cost of your transactions. For example, use calldata instead of memory where possible.
  • Reentrancy attacks: Be very careful about reentrancy attacks. Use reentrancy guards to prevent them. I initially tried a pattern without a guard and luckily a teammate pointed it out before it hit prod.
  • Integer overflows/underflows: Use SafeMath to prevent integer overflows and underflows. Solidity 0.8.0+ has built-in protection but it's still good to be aware of.
  • Ignoring the tests: I initially underestimated the importance of tests. Don't be like me. Write tests for everything.

The Sweet Smell of Success (and the Lingering Fear of Bugs)

After weeks of hard work, debugging, and countless cups of coffee, I finally had a working prototype of a custom stablecoin lending protocol based on Compound V3. It was a huge accomplishment, and my client was thrilled.

But even now, I'm constantly monitoring the protocol and looking for potential bugs. The DeFi space is constantly evolving, and new vulnerabilities are discovered all the time.

Next Steps: The Road Ahead

This tutorial is just the beginning. There's so much more to explore. Here are some things you might want to investigate:

  • Advanced risk management techniques: Implementing more sophisticated risk management strategies to protect your protocol from losses.
  • Decentralized governance: Allowing the community to control the protocol through a DAO.
  • Cross-chain lending: Expanding your protocol to other blockchains.

I'm currently exploring integrating Chainlink oracles for more accurate price feeds. I think that's the next big step for my protocol.

Final Thoughts: Embrace the Chaos (and Write Tests)

Forking Compound V3 and building a custom stablecoin lending protocol is a challenging but rewarding experience. It's not for the faint of heart. But if you're willing to put in the work, you can create something truly amazing.

Just remember to write tests, be careful with gas optimization, and learn from my mistakes. And most importantly, don't be afraid to ask for help. The DeFi community is full of smart, helpful people who are willing to share their knowledge. This approach has served me well in production environments (after all those bug fixes, of course!). I hope this saves you the debugging time I spent. Good luck, and happy coding!